1. Field of the Invention
This invention is related to dock equipment and in particular to dock levelers. It is specifically related to a mechanical device which automatically returns the deck to a horizontal dock position.
2. Prior Art
Dock levelers are used to bridge the gap between a loading dock and a vehicle bed. They typically employ a pivotally mounted deck having a pivoted lip at the distal end. The dock leveler operates in a number of modes, the normal one being where the lip is extended and resting on the bed of the vehicle. When the loading operation is completed it is preferred that the operator return the dock leveler to the stored horizontal position. If the operator does not restore the dock leveler, the lip will fall pendant when the vehicle leaves the dock, and if the tip of the lip is above the top of the lip keepers when the lip falls, the leveler will be supported by the lip resting in the lip keepers. However, if the leveler is not above the horizontal position when the lip falls, the lip will be outside the keepers and a potentially hazardous condition will be created. The dock leveler may appear to be in the horizontal stored position, but if a load is placed on the leveler, it will fall to the lowest position causing the load to be pitched forward into the driveway with serious risk of damage to goods and injury to personnel. It is desirable to return the deck automatically to the horizontal position if the vehicle leaves the dock before the leveler is restored, i.e. automatically returning to the dock position.
However another condition of operation is the so called "below dock end loading" position where the deck is pivoted downward and the lip is in a retracted position. This mode is typically used at the end of a loading sequence or beginning of an unloading sequence where the vehicle is nearly fully loaded and the lip can no longer remain in contact with the bed. The dock leveler must be maintained in this position without activating the automatic return mechanism.
Techniques are known for achieving automatic return to dock position. For example, U.S. Pat. No. 3,579,696 uses the position of the lip to control the raising of the deck assembly from the below dock position. Other dockboard designs having different mechanical implementations are found in U.S. Pat. Nos. 5,205,010; 5,392,481 and 5,416,941. Some of these systems are used in conjunction with hydraulic actuators while others use counterbalance and complex lever mechanisms.